Method for determining particular species of chlorine in a water sample

ABSTRACT

A technique for determining and distinguishing between specific species of chlorine in a supply of water is disclosed herein along with certain applicable apparatus. In carrying out this technique, one or more water samples are obtained from a larger supply and made to display a pH within a specific range. In a preferred embodiment, a sample is provided for each of the different species of chlorine to be determined. A predetermined amount of hydrogen peroxide is added to each of these samples. If hypochlorous acid and/or hypochlorite (one of the species to be determined) is present in any of the samples, the hydrogen peroxide by itself will react therewith for producing oxygen. If however either monochloramine or dichloramine (other chlorine species) is present, it is necessary to combine the hydrogen peroxide with a certain minimum amount of iodine, preferably in the form of potassium iodide, to produce an oxygen evolving reaction. Dichloramine requires a greater concentration of iodine than monochloramine and, hence, the two can be distinguished from one another. In each case, the produced oxygen is detected for determining whether any or all of these chlorine species are present in the water supply and the amounts thereof.

The present invention relates generally to techniques for analyzinggiven water supplies for chlorine and more particularly to a techniquefor determining and distinguishing between different specific species ofchlorine in the water supplies.

From a water conservation standpoint and particularly for the purpose ofprotecting fresh water fish it has been found desirable to monitor forspecific species of chlorine. Of particular interest are hypochlorousacid and/or hypochlorite (depending upon the pH of the water),monochloramine and dichloramine. It is therefore a specific object ofthe present invention to provide an uncomplicated, reliable and yeteconomical technique for determining and distinguishing between thesethree species of chlorine in a water supply.

Another specific object of the present invention is to provide atechnique for determining and distinguishing between the particularchlorine species mentioned on a large scale so as to be practical foruse by industries producing chlorine containing wastewater.

A more general object of the present invention is to provide a techniquefor determining a single specie of chlorine in a water sample,specifically a chlorine specie which reacts with hydrogen peroxide toproduce oxygen, with or without the need for certain other additives.

As will be described in more detail hereinafter, the technique disclosedherein is one which requires providing one and preferably more than onewater sample from the larger water supply being analyzed and maintainingthese samples at a pH within a specific range, preferably between fiveand eight. A predetermined amount of hydrogen peroxide is added to thesample for causing the latter to react with the particular chlorinespecie being sought, if the latter is present, to produce oxygen in thewater sample or samples, preferably only dissolved oxygen. Ifhypochlorous acid and/or hypochlorite, its equivalent (depending uponthe pH of the sample or samples), is present, the hydrogen peroxide willreact therewith to produce the resultant oxygen without the need forother additives. On the other hand, if either monochloramine ordichloramine is present, for the latter to react with hydrogen peroxideto produce oxygen, it has been found necessary to add certain minimumamounts of iodine, preferably in the form of potassium iodide. In thecase of dichloramine, a greater amount of iodine is necessary to producethe desired reaction than for monochloramine, depending upon thespecific pH of the water sample. In any event, a suitable device isprovided for detecting the oxygen if produced. In a preferred, practicalembodiment a separate water sample is provided for each of the speciesbeing analyzed.

The present technique for determining and distinguishing betweendifferent species of chlorine in one or more water samples will bedescribed in more detail hereinafter in conjunction with the drawingswherein:

FIG. 1 is a block diagram illustrating one technique for determining anddistinguishing between particular species of chlorine in individualwater samples;

FIG. 2 is a graphic display illustrating the detection of the specificchlorine species sought in the technique shown in FIG. 1;

FIG. 3 is a block diagram illustrating a second technique fordetermining said distinguishing between the same chlorine speciesassociated with the FIG. 1 technique but using a single water sample;

FIG. 4 is a diagrammatic illustration of a preferred system fordetermining and distinguishing between particular species of chlorine inan overall water supply and specifically a system which is especiallysuitable for use on a large scale; and

FIG. 5 is a view in vertical section of an oxygen sensing devicecomprising one component of the overall system shown in FIG. 4.

As stated briefly above and as will be described in more detailhereinafter, the present invention utilizes hydrogen peroxide (H₂ O₂) asa primary component in determining and distinguishing between certainspecies of chlorine in a water supply. These chlorine species consist ofhypochlorous acid and/or hypochlorite, monochloramine and dichloramine.In the case of hypochlorous acid and/or hypochlorite, thechlorine/hydrogen peroxide reaction is believed to involve the followingsteps:

    H.sub.2 O.sub.2 +HOCl⃡HOOCl+H.sub.2 O          (1)

    HOOCl→H.sup.+ +O.sub.2 +Cl.sup.-                    (2)

In reaction step (1) above, whether hypochlorous acid and/orhypochlorite is present in the water sample depends upon the pH of thelatter. If the pH is about eight or greater, hypochlorite will bepresent for the most part with little if any hypochlorous acid. At lowerpH values, greater amounts of hypochlorous acid is present as opposed tohypochlorite. In this regard, since hypochlorite and hypochlorous acidare actually one in the same specie depending upon the pH of the watersample, for purposes of simplicity both will be referred to merely ashypochlorite with the understanding that the two may be present, eitheralone or together, depending upon the pH of the particular water samplein question. In any event, this specific chlorine specie is reduced byhydrogen peroxide to ultimately produce oxygen, without the need for anyother additives, as seen in reaction step (2). As a result of thisreaction, a suitable device can be provided for detecting the oxygen andthereby monitoring the presence or absence of hypochlorous acid and/orhypochlorite, as will be discussed in more detail hereinafter. In apreferred embodiment of the present invention, the amount of hydrogenperoxide initially provided is selected so that all of the oxygenproduced is dissolved in the water sample so that an appropriate device,specifically a commercially available amperometric oxygen probe can beused to detect the dissolved oxygen (referred to as pO₂ ) if present andthe quantity present. In this latter regard, it is important todetermine the quantity of oxygen produced since this value correspondsdirectly to the amount of hypochlorite in the sample. More specifically,as will be discussed in more detail below, it has been found that thesteady state production of oxygen (ΔpO₂) and the initial rate response(ΔpO₂ /sec) are directly related to chlorine concentration. Because ofthis, it should be apparent that the measurements must be carried outunder anaerobic reaction conditions.

In performing various analytical tests relating to the reaction ofhydrogen peroxide and hypochlorite, it was not only determined thatthere is a quantitative relationship between the hypochlorite presentand the dissolved oxygen produced but that both the steady state andinitial rate measurements are strongly pH dependent, so long as the pHof the water sample is at approximately eight or below. Within this pHrange the greatest increase occurs between a pH of five and eight.Beyond a pH of eight, the O₂ formation reaction is pH independent andhence is preferred. In any event, it has been found desirable to controlthe pH of the sample, preferably at a fixed value between a pH of fiveand eight and most preferably at a pH of about eight. This may beaccomplished by providing a standard buffer solution at the desired pHand combining this solution in sufficient quantity with the sample inquestion so that the latter (e.g. the combination) displays the same pH.

In further evaluating the reaction between hydrogen peroxide and watersamples containing hypochlorite, it was found that at a fixed hydrogenperoxide concentration (1.0 mM), the increase in steady state pO₂changes linearly with hypochlorite solution. Initial rate experimentscarried out at a constant hydrogen peroxide concentration and variablehypochlorite concentration were used to generate log (initial rate)versus log (HOCl) plots. These plots exhibited a slope of 1.0 forsamples at both a pH of eight and at a pH of five, indicating that thereaction is indeed first order with respect to hypochlorite species. Asimilar experiment was carried out for a constant HOCl concentration anda variable hydrogen peroxide concentration. The results of the latterexperiment indicated a first order reaction with respect to the hydrogenperoxide.

With further reference to the reaction between hydrogen peroxide andhypochlorite, it has been found that a preferred technique fordetermining whether or not hypochlorite is present in a water sample(and the amount if present) utilizes a sufficient amount of hydrogenperoxide to provide a concentration level of 10⁻³ M. In this preferredtechnique, the sample itself is maintained at a pH of eight in aphosphate buffer. Responses to hypochlorite using this technique wereobserved down to 0.03 ppm Cl in the sample tested. An upper detectionlimit of approximately 75 ppm Cl has also been observed. This upperdetection limit is due to oxygen solubility limitations, i.e., at [OCl⁻] greater than 75 ppm, the solution becomes oxygen saturated, resultingin additionally produced oxygen leaving the solution. If the overalldetection scheme is capable of not only measuring the dissolved oxygenbut also free oxygen gas in the case where the sample is saturated, thepresent technique would not necessarily be confined to an upper limit.

In contrast to the foregoing reaction between hydrogen peroxide andhypochlorite (or hypochlorous acid), no reaction occurs between hydrogenperoxide and either monochloramine or dichloramine in the absence ofiodine, preferably in the form of potassium iodide (KI). Morespecifically, it has been found that in the presence of small amounts ofpotassium iodide (10⁻³ M), monochloramine rapidly oxidizes hydrogenperoxide. In the presence of monochloramine and potassium iodide, thehydrogen peroxide oxidation reaction is believed to involve thefollowing steps:

    NH.sub.2 Cl+2I.sup.- H.sup.+ I.sub.2 +NH.sub.4.sup.+ +Cl.sup.-(3)

    I.sub.2 +H.sub.2 O.sub.2 →O.sub.2 +2I.sup.- +2H.sup.+(4)

From reaction step (4) above, it should be apparent that the reactionjust described results in the production of oxygen gas. In initial workdone in this area, it was found that at fixed hydrogen peroxide andpotassium iodide concentrations, the initial rate response (ΔpO₂ /sec)as well as the steady state response (ΔpO₂) were found to changelinearly with monochloramine concentration. At fixed hydrogen peroxideand monochloramine concentrations, the initial rate of ΔpO₂ was found tobe linearly related to the potassium iodide concentration whereas thesteady state response was found to be independent of potassium iodideconcentration. In the absence of monochloramine, no O₂ was generated ina buffer solution (pH 8.0) containing both hydrogen peroxide andpotassium iodide. Initial rate experiments carried out at constant H₂ O₂and KI concentrations with variable NH₂ Cl concentrations were used togenerate log (initial rate) versus log (NH₂ Cl) plot. The plot exhibiteda slope of 1.0 at pH 8.0, indicating that the reaction is first orderwith respect to NH₂ Cl. In addition, in this initial work, it waslearned that monochloramine and dichloramine can be differentiated bythe pH of the sample containing these chlorine species and the potassiumiodide concentration provided.

In subsequent experiments it was observed that a linear signal(quantities of oxygen produced) is generated in accordance with theconcentration level of the monochloramine for concentrations rangingfrom 0.08 to 5 ppm Cl. The signal measured for monochloramine has beenfound to have no contribution for dichloramine so long as the potassiumiodide concentration level remains at or below a certain level,specifically about 10⁻³ M in the samples tested. On the other hand, byproviding a greater concentration of potassium iodide, specifically aconcentration level of about 5×10⁻² M, in a sample displaying a pH ofabout eight, the dichloramine, if present, reacts with the hydrogenperoxide to produce oxygen in the same manner as monochloramine andhypochlorite. In an actual example, a water sample having dichloraminetherein was maintained at a pH of 8.0 using a phosphate buffer andsufficient hydrogen peroxide was provided to maintain a concentrationlevel of 10⁻³ M. In addition, sufficient potassium iodide was providedfor maintaining a concentration level of about 10⁻² M. This resulted inthe observation of a linearity of signal versus concentration ofdichloramine from 0.2 to 0.7 ppm Cl.

With further reference to the reaction between hydrogen peroxide and thechloramine species, it should be apparent that both can be distinguishedfrom hypochlorite (or hypochlorous acid) by adding a certain minimumamount of iodine to the sample. It should also be apparent thatmonochloramine and dichloramine can be distinguished from one another bythe amount of iodine used. While an exact amount of iodine and hydrogenperoxide necessary to accomplish this along with a particular pH of thesolution have been suggested, it should be apparent that variations ofone or all of these parameters will cause the others to vary. Forexample, a lower pH than eight for the solution may cause a change inthe concentration levels of potassium iodide necessary to make theappropriate distinctions. Nevertheless, one could readily determinethese parameters based on the teachings herein.

Having described the foregoing ways of determining and distinguishingbetween the three specific chlorine species discussed above in a watersample, attention is now directed to various suggested systems forcarrying out this technique. To this end, reference is first made toFIG. 1 which illustrates one such system generally designated by thereference numeral 10. As seen there, this system includes three distinctwater samples S-1, S-2 and S-3 which may be taken from a single largersupply (not shown). Each of these samples is combined with a buffersolution to maintain its pH at a desired level, for example at eight, asindicated in FIG. 1. In the case of sample S-1, the prescribed amount ofhydrogen peroxide alone is added thereto. This particular solution isfree of any iodine. As a result, only the hypochlorite and/orhypochlorous acid, if present, and the hydrogen peroxide react toproduce the previously described oxygen. In the case of sample S-2, bothhydrogen peroxide and potassium iodide in the prescribed amounts areintroduced therein for causing the hypochlorite and/or monochloramine,if present, to react with the hydrogen peroxide to produce its ownresultant oxygen. Finally, in the case of the sample S-3, the prescribedamounts of hydrogen peroxide and potassium iodide are provided thereinfor causing the hypochlorite, monochloramine and dichloramine to reactwith the hydrogen peroxide for producing its own oxygen.

System 10 also includes an oxygen detector 12 which will be discussed inmore detail hereinafter with respect to FIGS. 4 and 5. For the moment,it should suffice to say that this detector serves to detect oxygenproduced as a result of the previously described reactions in samplesS-1, S-2 and S-3. In this regard, in order to not only determine whichif any of the three previously described chlorine species is present inthe water supply used to provide the samples but also the quantitiesthereof, it is necessary to evaluate each of the samples separately.This is because the oxygen generated as a result of the presence of thespecies are additive. More specifically, when hydrogen peroxide alone isadded to the sample S-1, a specific amount of oxygen is generated,depending upon the amount of hypochlorite and/or hypochlorous acidpresent. In the graphic illustration of FIG. 2 which shows time versusthe peak oxygen level detected by detector 12, the first three peakscorrespond to the amount of oxygen detected as a result of the reactionin sample S-1. Note that this peak value is indicated at A. Thereafter,when the prescribed amounts of hydrogen peroxide and potassium iodideare added to sample S-2, the amount of oxygen detected is shown in FIG.2 to be equal to the level A+B, that is, an amount A contributed by thehypochlorite present and an amount B contributed by the monochloramine.In sample S-3, when the prescribed amounts of hydrogen peroxide andpotassium iodide are added, the total amount of oxygen detected isA+B+C, that is, an amount A corresponding to the hypochlorite in thesample, an amount B corresponding to the monochloramine in the sampleand an amount C corresponding to the amount of dichloramine.

From the foregoing, it should be apparent that if the graphicillustration of FIG. 2 represents oxygen generating reactions sufficientto depleat reproducible amounts of the reacting chlorine species in thevarious samples S-1, S-2 and S-3, a quantitative analysis of thesespecies can be made. More specifically, from the analysis of sample S-1,the exact amount of hypochlorite and/or hypochlorous acid can bedetermined. From sample S-2, the amount of this latter specie andmonochloramine together can be determined and therefore, based on theresults of sample S-1, the amount of monochloramine alone can bedetermined. In the same manner, from sample S-3, the amount ofdichloramine alone can be determined. As stated above, each sample mustbe maintained at a specific pH, preferably at about eight, a sufficientamount of hydrogen peroxide must be provided and the proper amount ofpotassium iodide must also be used, depending upon whethermonochloramine or dichloramine is being sought.

Referring to FIG. 3, attention is directed to a second system 14 foraccomplishing the same end result as system 10, that is, for determiningand distinguishing between the three previously described chlorinespecies in a water supply. In system 14, a single sample S-1 isinitially provided at a precontrolled pH level, as indicateddiagrammatically by the pH buffer added thereto. Like system 10, thesample S-1 in system 14 is combined with only hydrogen peroxide (in theabsence of potassium iodide) so to cause an oxygen producing reactionbetween the hydrogen peroxide and hypochlorite, if the latter ispresent. The oxygen produced is detected by the same type of detector 12used in system 10 and the results may be graphically illustrated in thesame manner shown in FIG. 2, e.g. as the level A shown there. However,instead of providing second and third distinct samples as in system 10,system 14 uses the same sample S-1 to detect for monochloramine anddichloramine. In the case of monochloramine, after the hypochlorite hasbeen detected for, hydrogen peroxide in the prescribed amount is againprovided in the sample (assuming an excess amount was not initiallyadded) in combination with the prescribed amount of potassium iodide forcausing all of the monochloramine to react therewith for producingoxygen. This oxygen is also detected but unlike system 10, the amountdetected in system 14 corresponds only to the monochloramine (amount Bin FIG. 2) since the hypochlorite has already been exhausted. In orderto test for dichloramine, the same sample is thereafter provided withstill another prescribed amount of hydrogen peroxide (again assuming anexcess is not present) in combination with the prescribed amount ofpotassium iodide for causing all of the dichloramine in the sample toreact for producing oxygen. This oxygen is detected and corresponds onlyto the amount of dichloramine present in the sample (e.g., the amountC).

Referring now to FIG. 4, attention is directed to still another systemfor determining and distinguishing between the previously describedchlorine species and specifically a system which is especially suitablefor use in large scale. This system which is generally indicated by thereference numeral 16 includes a reservoir 18 for containing a watersample to be analyzed therein. This container may be designed to house adiscrete sample or, as indicated diagrammatically at 20, it may bedesigned for housing a continuously periodically replenished sample froma larger water supply not shown. A separate reservoir 22 containing abuffer solution at a predetermined pH is placed in fluid communicationwith container 18 for combining the buffer solution with the sample formaintaining the pH level of the combination at a predetermined level,for example at a pH of eight.

A subsample of the combination sample just described is pumped orotherwise conveyed through tube means 19 by suitable means 24 into aninjection valve 26. As shown in FIG. 4, the means 24 is a peristalticpump. The injection valve may be constructed of any suitable meanscapable of injecting hydrogen peroxide and/or potassium iodide into thesubsample as the latter passes therein. In a preferred embodiment,system 16 includes three separate and distinct reservoirs 28, 30 and 32for respectively containing hydrogen peroxide alone, hydrogen peroxidein combination with potassium iodide (at a prescribed concentrationlevel) and hydrogen peroxide in combination with potassium iodide (at adifferent prescribed concentration level). Suitable means generallyindicated at 34 including an appropriate metering valve generallyindicated at 36 and control components (not shown) are provided foralternatively placing the three reservoirs 28, 30 and 32 in fluidcommunication with the injection valve 26 for selectively meteringpredetermined amounts of the additives contained in these reservoirsinto the subsample passing into the injection valve. For example, in thecase of a first subsample, the valve 36 can be controlled to cause theprescribed amount of hydrogen peroxide from reservoir 28 to be injectedinto the subsample as the latter passes into the injection valve. At thesame time, the buffer could and preferably would be combined with thesubsamples at valve 26 rather than at reservoir 18, as indicated bydotted lines in FIG. 4. The means 24 thereafter causes the subsample topass into oxygen sensor 38 which will be described in more detail withrespect to FIG. 5. This oxygen sensor serves to detect the amount ofoxygen produced as a result of the reaction between the hydrogenperoxide and any hypochlorite in the subsample. A conventionalpotentiostat 40 is coupled to the sensor and serves as a transducer forconverting the detected oxygen to an electrical current which, in turn,is used to drive a readout 42 for providing a visual and/or permanentdisplay corresponding to the amount of oxygen detected. The firstsubsample is thereafter pumped or otherwise delivered into a wastecontainer 44.

Having quantitatively analyzed the first subsample of water forhypochlorite, as described above, pump 24 serves to direct a secondsubsample through to injection valve 26. At the same time, means 34controls metering valve 36 so as to cause the prescribed amount ofhydrogen peroxide and potassium iodide to be injected from the reservoir30 into the injection valve so as to mix with the second subsample. Thissecond subsample then passes into the oxygen sensor 38 where the oxygengenerated thereby is detected and readout. The second subsample is thenpumped into waste container 44. This procedure is again repeated for athird subsample. However, in this latter case, means 34 causes theinjection valve 36 to inject the prescribed amount of hydrogenperoxide/potassium iodide from container 32 into the injection valvewhile the third sample is therein. This mixture is immediatelythereafter pumped into the oxygen sensor where the generated oxygen isdetected and readout. Finally, the third sample is pumped into wastecontainer 44.

From the foregoing, it should be apparent that overall system 16functions in the same way as previously described system 10 to providecorresponding levels of detected oxygen A, A+B and A+B+C so thathypochlorite, monochloramine and dichloramine can be quantitativelydetermined.

Referring now to FIG. 5, attention is directed to a specific oxygensensor which, as stated previously, is preferably a commerciallyavailable amperometric oxygen probe. This probe is shown including astainless steel base 46 defining an inner chamber 48 in the form of athrough channel for receiving and passing therethrough the previouslydescribed subsamples of water from container 18. In this regard,opposite ends of the chamber 48 are placed in fluid communication withenlarged, internally threaded bores 50 adapted to receive cooperatingends of tube means 19 serving to carry the flow of sample water asdescribed above.

Probe 38 includes a main body 52 fixedly connected with base 46 forcontaining an oxygen permeable membrane 54 and the previously describedpotentiostat 40. The membrane itself is constructed of a suitablematerial, for example Teflon (a trademark of DuPont) and extendsentirely across the bottom opening of an overall chamber 56 defined byspace 46 in combination with main body 52. The membrane cooperates withthe subsample located within chamber 48 to cause the oxygen producedtherein to pass into chamber 56.

Potentiostat 40 is located within chamber 56 and is comprised of ananode 58, a cathode 60 and an aqueous solution of potassium chloride 62within its own container 64. These components in conjunction withsuitable electronic components (not shown) contained within housing 66convert the oxygen entering chamber 56 into a corresponding parentsignal for driving previously recited readout 42.

At stated previously, the entire probe and potentiostat belong with thereadout device and previously described pump 24 and injection valve 26may be conventional components. This is equally true of means 34including its metering valve 36 and the control means associatedtherewith. Moreover, while not shown, a suitable means for detecting O₂gas (out of solution) could be readily provided if the samples areanalyzed in excess of their O₂ saturation levels.

What is claimed is:
 1. A method for determining a particular specie ofchlorine in a water sample, said method comprising the steps of:providing said sample at a pH within a specific range; adding apredetermined amount of hydrogen peroxide to said sample for causing thelatter to react with said chlorine specie if present to produce oxygen;and detecting said oxygen if produced for indicating the presence ofsaid specie.
 2. A method according to claim 1 wherein the chlorinespecie to be determined is hypochlorous acid and/or hypochloritedepending upon the pH of said water sample and wherein said water sampleis provided without and is free of potassium iodide whereby todistinguish said hypochlorous acid and/or hypochlorite if present frommonochloramine and dichloramine if the latter two chlorine species alsohappen to be present in said sample.
 3. A method according to claim 2wherein said sample is provided at a pH of between five and eight.
 4. Amethod according to claim 3 wherein said hydrogen peroxide is providedin said water sample at a concentration of about 10⁻³ M.
 5. A methodaccording to claim 1 wherein the chlorine specie to be determined is oneof monochloramine or dichloramine and wherein a predetermined amount ofpotassium iodide is added to said water sample whereby to detect saidmonochloramine or dichloramine species if present from hypochlorous acidand/or hypochlorite if the latter chlorine specie also happens to bepresent in said sample.
 6. A method according to claim 5 wherein saidsample is provided at a pH of between about five and eight.
 7. A methodaccording to claim 6 wherein said potassium iodide is provided in saidwater sample at one of two different specific concentration levelswhereby to detect for a specific one of said monochloramine anddichloramine species.
 8. A method according to claim 7 wherein thechlorine specie to be determined is monochloramine and wherein theconcentration level of potassium iodide provided in said water sample isabout 10⁻³ M.
 9. A method according to claim 7 wherein the chlorinespecie to be determined is dichloramine and wherein the concentrationlevel of potassium iodide provided in said water sample is about 10⁻² M.10. A method according to claim 1 wherein all of said oxygen producedincludes oxygen which is dissolved in said sample and wherein saiddetecting means includes for detecting said dissolved oxygen.
 11. Amethod according to claim 10 wherein said oxygen produced consists ofsaid dissolved oxygen.
 12. A method for determining chlorine speciesfrom a group consisting of hypochlorous acid and/or hypochlorite,monochloramine and dichloramine in respective first, second and thirdsamples of a larger supply of water, said method comprising the stepsof: providing each of said samples at a pH within a specific range;placing a predetermined amount of hydrogen peroxide in each of saidsamples; providing said first sample free of potassium iodide wherebysaid hypochlorous acid and/or hypochlorite if present will react withsaid hydrogen peroxide to produce oxygen but said monochloramine anddichloramine if also present will not react with said hydrogen peroxideto produce oxygen; placing a first predetermined amount of potassiumiodide in said second water sample for causing said monochloramine andnot said dichloramine to react with said hydrogen peroxide and potassiumiodide for producing additional oxygen; placing a second predeterminedamount of potassium iodide in said third water sample for causing saiddichloramine to react with said hydrogen peroxide and said potassiumiodide for producing still further oxygen; and detecting from each ofsaid sample oxygen for indicating whether or not any of said chlorinespecies are present in said water supply.
 13. A method according toclaim 12 wherein said each of said samples is provided at a pH ofbetween about five and eight and wherein said hydrogen peroxide isprovided in each of said samples at a concentration level of about 10⁻³M.
 14. A method according to claim 13 wherein said potassium iodide isprovided in said second sample at a concentration level of about 10⁻³ Mand in said third sample at a concentration level of about 5×10⁻² M. 15.A method according to claim 12 wherein all of said oxygen produced isdissolved in said samples and wherein said detecting means includesmeans for detecting said dissolved oxygen.
 16. A method according toclaim 12 wherein said samples are maintained at a particular pH by thestep of adding buffer solutions of said particular pH thereto insufficient quantities to cause the overall samples to display said pH.17. A method according to claim 16 wherein said particular pH is abouteight.
 18. A method for determining chlorine species from a groupconsisting of hypochlorous acid and/or hypochlorite, monochloramine anddichloramine in a single sample of water, said method comprising thesteps of: providing said sample at a pH within a specific range; placinga predetermined amount of hydrogen peroxide in said sample; thereafter,initially maintaining said sample free of potassium iodide whereby saidhypochlorous acid and/or hypochlorite if present will react withhydrogen peroxide to produce an initial amount of oxygen but saidmonochloramine and dichloramine if also present will not react with saidhydrogen peroxide to produce an initial amount of oxygen; detecting forsaid initial amount of oxygen to indicate the presence or absence ofsaid hypochlorous acid and/or hypochlorite; thereafter placing a firstpredetermined amount of potassium iodide in said water sample forcausing said monochloramine and not said dichloramine to react with saidhydrogen peroxide and potassium iodide for producing a second,additional amount of oxygen; detecting for said additional amount ofsaid oxygen if present to indicate the presence or absence ofmonochloramine; thereafter placing a second predetermined amount ofpotassium iodide in said water sample for causing said dichloramine toreact with said hydrogen peroxide and said potassium iodide forproducing a third amount of oxygen; and detecting for said third amountof oxygen if present to indicate the presence or absence of saiddichloramine.